CN115959657B - Natural graphite-based heat dissipation film and preparation method thereof - Google Patents
Natural graphite-based heat dissipation film and preparation method thereof Download PDFInfo
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- CN115959657B CN115959657B CN202310254883.8A CN202310254883A CN115959657B CN 115959657 B CN115959657 B CN 115959657B CN 202310254883 A CN202310254883 A CN 202310254883A CN 115959657 B CN115959657 B CN 115959657B
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- 230000017525 heat dissipation Effects 0.000 title claims abstract description 38
- 229910021382 natural graphite Inorganic materials 0.000 title claims abstract description 36
- 238000002360 preparation method Methods 0.000 title claims abstract description 24
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 207
- 229910002804 graphite Inorganic materials 0.000 claims abstract description 199
- 239000010439 graphite Substances 0.000 claims abstract description 199
- 239000000463 material Substances 0.000 claims abstract description 66
- 238000000034 method Methods 0.000 claims abstract description 58
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 claims abstract description 37
- 239000002253 acid Substances 0.000 claims abstract description 37
- 238000010438 heat treatment Methods 0.000 claims abstract description 29
- 238000002156 mixing Methods 0.000 claims abstract description 29
- QAOWNCQODCNURD-UHFFFAOYSA-N sulfuric acid Substances OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims abstract description 23
- 239000002002 slurry Substances 0.000 claims abstract description 19
- 239000002131 composite material Substances 0.000 claims abstract description 17
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- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 claims description 36
- 239000000203 mixture Substances 0.000 claims description 19
- 229910000147 aluminium phosphate Inorganic materials 0.000 claims description 18
- 239000011268 mixed slurry Substances 0.000 claims description 13
- 239000013067 intermediate product Substances 0.000 claims description 12
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- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 claims description 9
- 239000011593 sulfur Substances 0.000 claims description 9
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- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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Abstract
The invention provides a natural graphite-based heat dissipation film and a preparation method thereof. The method comprises the following steps: (1) puffing: adding hydrogen peroxide into concentrated sulfuric acid solution; mixing the first part of graphite return material with natural crystalline flake graphite and then mixing with the first part of mixed acid liquid; performing a first heat treatment; then washing until the pH is more than or equal to 5, and drying; scattering the first part of dried graphite blank, washing to neutrality, and drying; (2) film formation: mixing the second part of graphite return material with the second part of mixed acid liquid, and then performing second heat treatment; secondly, dispersing in an oil solvent; secondly, immersing the second part of dried graphite blank into oil-based slurry, and drying; secondly, pressing the composite graphite blank to obtain a natural graphite-based heat dissipation film; waste materials are also obtained in the pressing process and are smashed; and mixing the crushed expanded graphite with the graphite film leftover materials to obtain the graphite return material. The natural graphite-based heat dissipation film has the advantages of high density, high heat conductivity, mild preparation process, low product price and stable performance.
Description
Technical Field
The invention relates to the field of graphite film materials, in particular to a natural graphite-based heat dissipation film and a preparation method thereof.
Background
In recent years, the demand for high-end heat dissipation materials is increasing, and various heat dissipation materials are also layered endlessly. Especially, new technologies such as 5G and the like are continuously advanced in recent years, the power consumption of electronic equipment is continuously increased, the demand for high heat conduction materials is rapidly increased, the market in the electronic field reaches the billion level, and the heat conduction requirements of electronic devices are more and more difficult to meet due to the fact that the heat conductivity of traditional metal heat conduction materials such as pure aluminum and pure copper is 237W/(m.k) and 401W/(m.k).
The graphite heat dissipation material is used as an emerging heat conduction material, has the characteristics of high temperature resistance, light weight, high heat conductivity, strong chemical stability and the like, and is beneficial to miniaturization, microminiaturization and high power of electronic instruments and equipment.
However, the traditional natural graphite paper has the highest thermal conductivity which can only reach about 250W/(m.K), and has low thermal conductivity, so that the use requirement of high-end electronic products cannot be met; and the artificial graphite film prepared from materials with good heat conducting property, such as PI film (polyimide), has the PI raw material monopoly in the United states and Japan, restricts the development of related industries and seriously affects national security.
In addition, the PI film is limited by the shrinkage cracking characteristic of the PI film in the graphitization process, and the achievable thickness range is narrow, which also limits the development of PI artificial graphite films, and the cost of the artificial graphite films is high due to the influence of raw materials and graphitization process. The preparation process of the graphene heat dissipation film is complex, so that the graphene heat dissipation film is high in price, and a large amount of waste gases such as sulfur, nitrogen or chlorine and a large amount of waste water are generated in the production process of the graphene heat dissipation film, so that the environment is polluted.
According to the invention, natural crystalline flake graphite is used as a raw material, and a unique mild expansion method is adopted to prepare the multilayer graphene/graphite composite material, so that the energy consumption is reduced, and the protection effect on the graphite crystal microstructure is achieved. In addition, waste gas is not generated in the production process, impurities in the waste water are less, the waste water is convenient to recycle, and leftover materials, waste materials and the like generated by the product can be recycled. The product prepared by the scheme has excellent heat radiation performance, but low price and low sulfur content.
Disclosure of Invention
The invention mainly aims to provide a preparation method of a high-density natural graphite-based heat dissipation film, which aims to solve the problems of low heat conductivity, low density and environment friendliness of a graphite film in the prior art.
In order to achieve the above object, according to one aspect of the present invention, there is provided a method for preparing a natural graphite-based heat dissipation film, characterized in that the preparation method comprises a swelling process and a film forming process performed sequentially; wherein, the puffing process comprises: adding hydrogen peroxide into the concentrated sulfuric acid solution to obtain mixed acid liquor, and dividing the mixed acid liquor into a first part and a second part; mixing the first part of graphite return material with natural crystalline flake graphite to obtain a mixture; mixing the mixture with a first part of mixed acid solution to obtain first mixed slurry; performing first heat treatment on the first mixed slurry to obtain an expanded graphite blank; washing the expanded graphite blank until the pH value is more than or equal to 5, and drying to obtain a dried graphite blank; dividing the dried graphite blank into a first part and a second part, scattering the first part of dried graphite blank, washing to be neutral, and drying to obtain expanded graphite fragments; the film forming process comprises the following steps: mixing a second part of graphite return material with a second part of mixed acid solution to obtain a second mixed slurry; performing second heat treatment on the second mixed slurry to obtain an intermediate product; dispersing the intermediate product in an oil solvent to obtain an oil slurry; immersing the second part of dried graphite blank into oil-based slurry, and drying to obtain a composite graphite blank; pressing the composite graphite blank to obtain a natural graphite-based heat dissipation film; wherein, the waste material of the natural graphite-based heat dissipation film is also obtained in the pressing process, and the method further comprises the following steps: crushing the waste to obtain graphite film leftover materials; the method comprises the steps of mixing crushed expanded graphite with graphite film scraps to obtain graphite return materials, and mixing the graphite return materials in any proportion, wherein the graphite return materials are divided into a first part of graphite return materials and a second part of graphite return materials.
Further, after the composite graphite blank is obtained, the film forming process further includes: carrying out third heat treatment on the composite graphite blank to obtain a graphite film intermediate; then, pressing the graphite film intermediate to obtain a natural graphite-based heat dissipation film; preferably, the third heat treatment is performed in an air atmosphere, and the treatment temperature is 350-450 ℃; alternatively, the third heat treatment is carried out under an inert atmosphere at a temperature > 450 ℃.
Further, the treatment temperature of the first heat treatment is 25-90 ℃, and the treatment time is 5 min-10 h; preferably, the expanded graphite blank is black sponge-like.
Further, the thickness of the natural graphite-based heat dissipation film is 50 μm-3 mm.
Further, in the mixed acid solution, the mass concentration of hydrogen peroxide is more than or equal to 20%, and the mass concentration of concentrated sulfuric acid solution is more than or equal to 90%; preferably, when hydrogen peroxide is added into the concentrated sulfuric acid solution, the mixing temperature is 0-15 ℃, and H in the hydrogen peroxide is more preferred 2 O 2 With H in concentrated sulfuric acid solution 2 SO 4 The molar ratio of (1) to (14:1).
Further, the mixed acid solution also comprises phosphoric acid; the mass concentration of phosphoric acid is more than or equal to 75%, the mixing temperature of phosphoric acid and hydrogen peroxide and concentrated sulfuric acid solution is 0-15 ℃, and H in phosphoric acid 3 PO 4 With H in concentrated sulfuric acid solution 2 SO 4 The molar ratio of (2) is more than or equal to 1:10.
Further, the volume ratio of the first part of mixed acid liquid to the second part of mixed acid liquid is (1:1) - (1:3).
Further, the mass ratio of the mixture to the first part of mixed acid liquid is (1:3) - (1:100).
Further, in the mixture, the mass ratio of the first part of graphite return material to the natural crystalline flake graphite is (1:0.05) to (1:0.15).
Further, the graphite return material is a mixture of expanded graphite scraps and graphite film scraps in any proportion.
Further, the mass ratio of the first part of dry graphite blank to the second part of dry graphite blank is (0.1:1) - (0.5:1).
Further, the mass ratio of the graphite return material of the second part to the mixed acid liquid of the second part is (1:8) - (1:100).
Further, the treatment temperature in the second heat treatment process is 25-90 ℃, and the treatment time is 5 min-10 h.
Further, the oil solvent is one or more of PVP, NMP and epoxy resin.
Further, in the oil-based slurry, the mass concentration of the intermediate product is 0.1-5%.
Further, the ratio of the second partially dried graphite blank to the oil-based slurry was 1g: (10-60) ml.
According to another aspect of the present invention, there is provided a natural graphite-based heat dissipation film prepared by the above preparation method; preferably, the density of the natural graphite-based heat dissipation film is 0.8-2.1 g/cm 3 The thermal conductivity is 400-720W/(mK), and the sulfur content is less than 1500ppm.
By applying the technical scheme of the invention, the high-density natural graphite-based heat dissipation film is prepared. The preparation method maximally utilizes the advantages of large grain size and few defects of the natural graphite, and the prepared multilayer graphene-like structure unit is complete, so that the prepared flexible graphite film has excellent heat conduction performance and is far superior to graphite paper prepared by the traditional method. The invention selects a specific mode for guiding the expansion and the repressing of the graphite flake, so that the preferred orientation degree of the graphite flake is high. The thickness of the graphite film product prepared by the technical scheme of the invention can reach 50 mu m-3 mm, and the problem that the thickness range of the PI artificial graphite film is narrow can be effectively solved. Meanwhile, the density of the graphite film product prepared by the method can reach 0.8-2.1 g/cm 3 The highest thermal conductivity can reach 600W/(m.K) above, and is far higher than that of the traditional material; in particular, the thermal conductivity of the graphite film prepared by the method is not greatly reduced along with the increase of the thickness of the product, and the use requirement of the graphite film can be fully met. In a word, the high-density natural graphite-based heat dissipation film prepared by the method has the advantages of high density, high heat conductivity, mild preparation process, low product price, stable performance and good market prospect.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention. In the drawings:
fig. 1 shows an optical photograph of an expanded graphite blank prepared according to example 1 of the present invention.
FIG. 2 shows a scanning electron micrograph of a cut surface of an expanded graphite film prepared according to example 1 of the present invention.
FIG. 3 shows a scanning electron micrograph of a section of a commercially available high temperature expanded graphite film of comparative example 2.
Detailed Description
It should be noted that, in the case of no conflict, the embodiments and features in the embodiments may be combined with each other. The invention will be described in detail below with reference to the drawings in connection with embodiments.
In order to solve the problems in the prior art as described above, the present invention provides a method for preparing a natural graphite-based heat dissipation film, which comprises a puffing process and a film forming process sequentially performed; wherein, the puffing process comprises: adding hydrogen peroxide into the concentrated sulfuric acid solution to obtain mixed acid liquor, and dividing the mixed acid liquor into a first part and a second part; mixing the first part of graphite return material with natural crystalline flake graphite to obtain a mixture; mixing the mixture with a first part of mixed acid solution to obtain first mixed slurry; performing first heat treatment on the first mixed slurry to obtain an expanded graphite blank; washing the expanded graphite blank until the pH value is more than or equal to 5, and drying to obtain a dried graphite blank; dividing the dried graphite blank into a first part and a second part, scattering the first part of dried graphite blank, washing to be neutral, and drying to obtain expanded graphite fragments; the film forming process comprises the following steps: mixing a second part of graphite return material with a second part of mixed acid solution to obtain a second mixed slurry; performing second heat treatment on the second mixed slurry to obtain an intermediate product; dispersing the intermediate product in an oil solvent to obtain an oil slurry; immersing the second part of dried graphite blank into oil-based slurry, and drying to obtain a composite graphite blank; pressing the composite graphite blank to obtain a natural graphite-based heat dissipation film; wherein, the waste material of the natural graphite-based heat dissipation film is also obtained in the pressing process, and the method further comprises the following steps: crushing the waste to obtain graphite film leftover materials; and mixing the crushed expanded graphite with the graphite film leftover materials to obtain graphite return materials, wherein the graphite return materials are divided into a first part of graphite return materials and a second part of graphite return materials according to any proportion. The preparation method in the technical scheme of the invention maximally utilizes the advantages of large grain size and few defects of the natural graphite, and the prepared multilayer graphene-like structure unit is complete, so that the prepared flexible graphite film has excellent heat conduction performance and is far superior to that of the conductive filmGraphite paper prepared by the method. The invention selects a specific mode for guiding the expansion and the repressing of the graphite flake, so that the preferred orientation degree of the graphite flake is high. The thickness of the graphite film product prepared by the technical scheme of the invention can reach 50 mu m-3 mm, and the problem that the thickness range of the PI artificial graphite film is narrow can be effectively solved. Meanwhile, the density of the graphite film product prepared by the method can reach 0.8-2.1 g/cm 3 The highest thermal conductivity can reach 600W/(m.K) above, and is far higher than that of the traditional material; in particular, the thermal conductivity of the graphite film prepared by the method is not greatly reduced along with the increase of the thickness of the product, and the use requirement of the graphite film can be fully met. In a word, the high-density natural graphite-based heat dissipation film prepared by the method has the advantages of high density, high heat conductivity, mild preparation process, low product price, stable performance and good market prospect.
In order to further enhance the thermal conductivity properties of the graphite film, it is preferable that the particle size of the natural crystalline flake graphite is 50 mesh and/or 32 mesh.
In actual operation, preferably, after the first heat treatment, the expanded graphite blank is removed entirely by the water float process. More preferably, the process of washing the expanded graphite blank to a pH of not less than 5 is achieved by spraying and suction filtration.
In order to further increase the density of the graphite film and simultaneously reduce the content of S, H, O and other impurities in the graphite film, in a preferred embodiment, after obtaining the composite graphite blank, the film forming process further comprises: carrying out third heat treatment on the composite graphite blank to obtain a graphite film intermediate; then, pressing the graphite film intermediate to obtain a natural graphite-based heat dissipation film; preferably, the third heat treatment is performed in an air atmosphere, and the treatment temperature is 350-450 ℃; alternatively, the third heat treatment is carried out under an inert atmosphere at a temperature > 450 ℃.
In order to further improve the heat conductivity and the density, in a preferred embodiment, the treatment temperature of the first heat treatment is 25-90 ℃ and the treatment time is 5 min-10 h; preferably, the expanded graphite blank is black sponge-like. The milder (less than 90 ℃) expansion technique is preferred, which is beneficial to better protect the crystalline structure of the crystalline flake graphite, thereby obtaining higher thermal conductivity and higher density.
In practice, the first heat treatment process described above is preferably carried out in an oven. The first mixed slurry was placed in a mold and capped with a cap prior to the first heat treatment. Then it was placed in an oven and allowed to stand until the graphite expanded into an intertwined worm-like shape (as shown in figure 1). The expanded graphite prepared according to the technical scheme of the invention is in a state of interlaced spongy, breaks through the limitation that the expanded graphite is in a low-density powder state in the traditional process, and reduces dust pollution.
In actual operation, the composite graphite blank is pre-pressed, and then the distance between the roller-to-roller spreader is gradually reduced, or the natural graphite-based heat dissipation film is finally prepared through a multi-stage spreader, wherein the thickness of the natural graphite-based heat dissipation film is 50 mu m-3 mm.
For the purpose of enabling the graphite to be further and sufficiently puffed, in a preferred embodiment, the mass concentration of hydrogen peroxide in the mixed acid solution is more than or equal to 20%, and the mass concentration of concentrated sulfuric acid solution is more than or equal to 90%; preferably, when hydrogen peroxide is added into the concentrated sulfuric acid solution, the mixing temperature is 0-15 ℃, and H in the hydrogen peroxide is more preferred 2 O 2 With H in concentrated sulfuric acid solution 2 SO 4 The molar ratio of (1) to (14:1).
For the purpose of enabling further sufficient expansion of the graphite, in a preferred embodiment, phosphoric acid is also included in the mixed acid solution; the mass concentration of phosphoric acid is more than or equal to 75%, the mixing temperature of phosphoric acid and hydrogen peroxide and concentrated sulfuric acid solution is 0-15 ℃, and H in phosphoric acid 3 PO 4 With H in concentrated sulfuric acid solution 2 SO 4 The molar ratio of (2) is more than or equal to 1:10. The phosphoric acid is added into the mixed acid liquid, so that the flake graphite is not excessively oxidized into a small lamellar structure in the process of being stripped, and the flexibility is small and the rigidity is strong because the pressed density of the graphite film is too high, and the phosphoric acid can be partially flexible.
In actual operation, it is preferable to drop the above-mentioned hydrogen peroxide solution into the stirred concentrated sulfuric acid solution, and then drop the phosphoric acid solution.
Preferably, the mass ratio of the first part of mixed acid liquid to the second part of mixed acid liquid is (1:1) - (1:3).
In order to enable the mixture to be more fully puffed, the mass ratio of the mixture to the first part of mixed acid liquid is (1:3) - (1:100).
In order to further improve the density of the graphite film, preferably, in the mixture, the mass ratio of the first part of graphite return material to the natural crystalline flake graphite is (1:0.05) - (1:0.15). The ratio is preferably favorable for reasonably constructing the ratio of the primary expanded graphite to the secondary expanded graphite in the graphite film.
In actual practice, the graphite return material is preferably a mixture of crushed expanded graphite and leftover materials of the graphite film in any proportion. More preferably, the particle size of the leftover material is 20 μm to 2cm, and the leftover material is crushed by a crusher. Means for preparing expanded graphite particles may be conventional in the art, for example, by breaking up with paddles.
In actual operation, the mass ratio of the first partially dried graphite blank to the second partially dried graphite blank is preferably (0.1:1) - (0.5:1). The first part of the dry graphite blank is used for crushing to obtain expanded graphite fragments, and the second part of the dry graphite blank is used for preparing a composite graphite blank with the oil-based slurry.
In order to make the secondary expanded graphite more fully expanded, in a preferred embodiment, the mass ratio of the second part of graphite return material to the second part of mixed acid solution is (1:8) - (1:100).
In order to make the secondary expanded graphite more fully expanded, in a preferred embodiment, the treatment temperature in the second heat treatment process is 25-90 ℃ and the treatment time is 5 min-10 h.
The choice of the oil-based solvent may be conventional in the art, e.g., the oil-based solvent is one or more of NMP, PVP, epoxy.
In order to make the proportion of the secondary expanded graphite in the composite graphite blank more reasonable, the mass concentration of the intermediate product in the oil-based slurry is preferably 0.1-5%.
In order to enable the oil-based slurry to be more fully absorbed, it is preferable that the ratio of the second partially dried graphite blank to the oil-based slurry is 1g: (10-60) ml.
According to another aspect of the present invention, there is provided a natural graphite-based heat dissipation film prepared by the preparation method as described above; preferably, the density of the natural graphite-based heat dissipation film is 0.8-2.1 g/cm 3 The thermal conductivity is 400-720W/(mK), and the sulfur content is less than 1500ppm.
The present application is described in further detail below in conjunction with specific embodiments, which should not be construed as limiting the scope of the claims.
Example 1:
1. puffing process
(1) Dripping 4.5ml of 30% hydrogen peroxide into 20ml of 98% concentrated sulfuric acid solution under stirring, dripping more than 0.6ml of 85% phosphoric acid solution, and mixing at 1 ℃;
(2) Uniformly mixing 0.8g of 30-mesh natural crystalline flake graphite with 0.2g of first part graphite return material (0.1 g of crushed expanded graphite and 0.1g of leftover material of a graphite film) to obtain a mixture;
(3) Placing the mixture into 19ml of mixed acid solution, fully and uniformly mixing, transferring the mixture into a mold, sealing a port, and placing the mold in a 35 ℃ oven for standing for 5 hours to obtain an expanded graphite blank;
(4) Taking out the whole expanded graphite blank by using a water float method, washing the expanded graphite blank to a pH value of 6.0 by a spray-suction filtration mode, and then drying in an oven, wherein the density of the expanded graphite blank is 0.0115g/cm 3 ；
2. Preparation of graphite film:
(1) Mixing the second part of graphite return material with 30ml of mixed acid solution, transferring and placing the mixture in a mold, sealing a mouth, placing the mold in a baking oven at 35 ℃ for standing for 5 hours, stirring and then performing ultrasonic dispersion to obtain an intermediate product;
(2) Dispersing the intermediate product in NMP solvent according to the mass concentration of 5%, and uniformly dispersing the intermediate product by an ultrasonic method to obtain oil-based slurry;
(3) Immersing the expanded graphite blank into 60ml of oil-based slurry (the concentration is 0.5%) until the slurry is fully absorbed, and then placing the slurry into an oven for fully drying to obtain a composite graphite blank;
(4) The composite graphite blank is placed in a nitrogen atmosphere furnace at 900 ℃ for heat treatment for 20min, then pre-pressed to 3mm, and then the expanded graphite blank is pressed into a graphite film with the thickness of about 150 mm by a twin roll spreader with the spacing of 1mm, 600um, 400um, 200um and 190 um.
The method comprises the following steps of: the final graphite film material has a mass of 1.071g, a size of 5.6X15.8 cm, a thickness of 160um and a density of 2.06g/cm 3 。
Tested by a heat conductivity coefficient measuring instrument of the relaxation-resistant LFA 467: the thermal diffusivity of the material product is 365.08mm 2 and/S, the thermal conductivity is 639W/(mK) by calculation.
The carbon-sulfur element analyzer tests show that: the sulfur content of the graphite film material product was 503ppm.
A scanning electron micrograph of a cut surface of the expanded graphite film obtained in example 1 is shown in FIG. 2.
Example 2:
the difference from example 1 is only that the mixed acid liquor is free of phosphoric acid, the remainder being made up by concentrated sulfuric acid.
The method comprises the following steps of: the density of the final graphite film material is 1.95g/cm 3 。
Tested by a heat conductivity coefficient measuring instrument of the relaxation-resistant LFA 467: the thermal diffusivity of the material product is 357.12mm 2 and/S, the thermal conductivity 592W/(m.K) is calculated.
The carbon-sulfur element analyzer tests show that: the sulfur content of the graphite film material product was 631ppm.
Example 3:
the difference from example 1 is only that the third heat treatment is carried out at a temperature of 400℃under an air atmosphere.
The method comprises the following steps of: the density of the final graphite film material is 2.02g/cm 3 。
Subjected to a thermal conductivity test of the relaxation-resistant LFA 467: the thermal diffusivity of the material product is 360.61mm 2 and/S, obtaining the thermal conductivity 619W/(m.K) through calculation.
The carbon-sulfur element analyzer tests show that: the sulfur content of the graphite film material product was 476ppm.
Comparative example 1:
1. puffing process
(1) Dripping 4.5ml of 30% hydrogen peroxide into 20ml of 98% concentrated sulfuric acid solution under stirring, dripping more than 0.6ml of 85% phosphoric acid solution, and mixing at 1 ℃;
(2) Placing 1.0g of 30-mesh natural crystalline flake graphite into 23.75ml of mixed acid solution, fully and uniformly mixing, transferring, placing into a mold, sealing a mouth, and placing into a baking oven at 35 ℃ for standing for 5 hours to obtain an expanded graphite blank;
(3) Taking out the whole expanded graphite blank by using a water float method, washing the expanded graphite blank to a pH value of 6.0 by a spray-suction filtration mode, and then drying in an oven, wherein the density of the expanded graphite blank is 0.0095g/cm 3 ；
2. Preparation of graphite film:
(5) Immersing the expanded graphite blank into 60ml of NMP solvent, and then placing the expanded graphite blank into an oven for fully drying;
(6) And (3) placing the product of the last step in a nitrogen atmosphere furnace at 900 ℃ for heat treatment for 20min, pre-pressing to 3mm, and then pressing the expanded graphite blank into a graphite film with the thickness of about 150 mu m by a twin-roll spreader with the spacing of 1mm, 600 mu m, 400 mu m, 200 mu m and 190 mu m.
The method comprises the following steps of: the final graphite film material has a mass of 0.998g, a size of 5.6X15.8 cm, a thickness of 160um and a density of 1.92g/cm 3 。
Subjected to a thermal conductivity test of the relaxation-resistant LFA 467: the thermal diffusivity of the material product is 350.21mm 2 and/S, the thermal conductivity is 572W/(mK) by calculation.
The carbon-sulfur element analyzer tests show that: the sulfur content of the graphite film material product was 821ppm.
Comparative example 2:
a scanning electron micrograph of a cut surface of a commercially available high temperature expanded graphite film is shown in FIG. 3. As can be seen from the figure, compared with the dense graphite film prepared according to the technical scheme of the present invention, there are many pores in the commercially available graphite film, and the density is also lower, thereby affecting the thermal conductivity performance.
From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:
by applying the technical scheme of the invention, the high-density natural graphite-based heat dissipation film is prepared. The preparation method maximally utilizes the advantages of large grain size and few defects of the natural graphite, and the prepared multilayer graphene-like structure unit is complete, so that the prepared flexible graphite film has excellent heat conduction performance and is far superior to graphite paper prepared by the traditional method. The invention selects a specific mode for guiding the expansion and the repressing of the graphite flake, so that the preferred orientation degree of the graphite flake is high. The thickness of the graphite film product prepared by the technical scheme of the invention can reach 50 mu m-3 mm, and the problem that the thickness range of the PI artificial graphite film is narrow can be effectively solved. Meanwhile, the density of the graphite film product prepared by the method can reach 0.8-2.1 g/cm 3 The highest thermal conductivity can reach 600W/(m.K) above, and is far higher than that of the traditional material; in particular, the thermal conductivity of the graphite film prepared by the method is not greatly reduced along with the increase of the thickness of the product, and the use requirement of the graphite film can be fully met. In a word, the high-density natural graphite-based heat dissipation film prepared by the method has the advantages of high density, high heat conductivity, mild preparation process, low product price, stable performance and good market prospect.
The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (9)
1. The preparation method of the natural graphite-based heat dissipation film is characterized by comprising a puffing process and a film forming process which are sequentially carried out; wherein,,
the puffing process comprises the following steps:
adding hydrogen peroxide into a concentrated sulfuric acid solution to obtain a mixed acid solution, and dividing the mixed acid solution into a first part and a second part; mixing the first part of graphite return material with natural crystalline flake graphite to obtain a mixture; wherein the mass ratio of the first part of graphite return material to the natural crystalline flake graphite is 1:4;
mixing the mixture with a first part of the mixed acid solution to obtain first mixed slurry;
performing first heat treatment on the first mixed slurry to obtain an expanded graphite blank;
washing the expanded graphite blank until the pH value is more than or equal to 5, and drying to obtain a dried graphite blank;
dividing the dried graphite blank into a first part and a second part, scattering the first part of the dried graphite blank, washing to be neutral, and drying to obtain expanded graphite fragments;
the film forming process comprises the following steps:
mixing a second part of graphite return material with a second part of the mixed acid solution to obtain a second mixed slurry;
performing second heat treatment on the second mixed slurry to obtain an intermediate product;
dispersing the intermediate product in an oil-based solvent to obtain an oil-based slurry;
immersing a second part of the dried graphite blank into the oil-based slurry, and drying to obtain a composite graphite blank;
performing third heat treatment on the composite graphite blank to obtain a graphite film intermediate; then, the graphite film intermediate is subjected to pressing treatment to obtain the natural graphite-based heat dissipation film;
wherein the third heat treatment is performed in an air atmosphere, and the treatment temperature is 350-450 ℃; or, the third heat treatment is carried out in an inert atmosphere, and the treatment temperature is more than 450 ℃;
wherein, waste materials of the natural graphite-based heat dissipation film are also obtained in the pressing process, and the method further comprises: crushing the waste to obtain graphite film leftover materials; and mixing the expanded graphite scraps with the graphite membrane scraps to obtain the graphite return material, wherein the graphite return material is mixed in any proportion and is divided into the first part of graphite return material and the second part of graphite return material.
2. The preparation method according to claim 1, wherein the treatment temperature of the first heat treatment is 25-90 ℃ and the treatment time is 5 min-10 h; the treatment temperature of the second heat treatment is 25-90 ℃, and the treatment time is 5 min-10 h.
3. The preparation method according to claim 1, wherein the mass concentration of the hydrogen peroxide in the mixed acid solution is more than or equal to 20%, and the mass concentration of the concentrated sulfuric acid solution is more than or equal to 90%;
when the hydrogen peroxide is added into the concentrated sulfuric acid solution, the mixing temperature is 0-15 ℃; h in the hydrogen peroxide 2 O 2 With H in the concentrated sulfuric acid solution 2 SO 4 The molar ratio of (1) to (14:1);
the mixed acid solution also comprises phosphoric acid; the mass concentration of the phosphoric acid is more than or equal to 75%, the mixing temperature of the phosphoric acid, the hydrogen peroxide and the concentrated sulfuric acid solution is 0-15 ℃, and H in the phosphoric acid 3 PO 4 With H in the concentrated sulfuric acid solution 2 SO 4 The molar ratio of (2) is more than or equal to 1:10.
4. A method according to any one of claims 1 to 3, wherein the volume ratio of the first portion of the mixed acid solution to the second portion of the mixed acid solution is (1:1) - (1:3).
5. A method according to any one of claims 1 to 3, wherein the mass ratio of the mixture to the first portion of the mixed acid solution is (1:3) - (1:100).
6. The preparation method according to any one of claims 1 to 3, wherein the mass ratio of the second part of graphite return to the second part of the mixed acid solution is (1:8) - (1:100); the graphite return material is a mixture formed by crushing the expanded graphite and leftover materials of the graphite film according to any proportion.
7. A method of producing according to any one of claims 1 to 3, wherein the mass ratio of the first portion of the dried graphite blank to the second portion of the dried graphite blank is (0.1:1) to (0.5:1).
8. A method of preparation according to any one of claims 1 to 3, wherein the oily solvent is one or more of PVP, NMP, epoxy resin; in the oil-based slurry, the mass concentration of the intermediate product is 0.1-5%; the ratio of the second part of the dry graphite blank to the oil-based slurry is 1g: (10-60) ml.
9. A natural graphite-based heat dissipation film prepared by the preparation method of any one of claims 1 to 8; the density of the natural graphite-based heat dissipation film is 0.8-2.1 g/cm 3 The thermal conductivity is 400-720W/(mK), and the sulfur content is less than 1500ppm.
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| CN102807845B (en) * | 2012-08-17 | 2014-12-03 | 叶全惠 | Preparation method for high heat conduction and radiation material by intercalating metal particles between layers of thin-layer graphene |
| JP5624647B2 (en) * | 2013-06-07 | 2014-11-12 | 株式会社カネカ | Method for producing graphite composite film |
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